I. INTRODUCTION
The power utility industry is required to transmit power over long distances, but is finding it increasingly difficult to secure rights of way for new transmission lines; this trend demands greater utilisation of existing transmission lines, but as lines become increasingly loaded they operate closer to instability. In many cases the limiting stability criterion is poor damping of the electromechanical oscillations of the generators that feed the transmission system [1]. The principal method of influencing these oscillations is through the excitation control systems of the generators (automatic voltage regulators and power system stabilisers). However, it has long been recognised that the damping of such oscillations can be further enhanced by dynamically altering the series impedance of one of the transmission lines in an interconnected power system using some form of controllable series capacitive compensator [2]. With the emergence of modern power-electronic-controlled compensators, these ideas have become practically feasible, and much work has been reported on the design of power oscillation damping control schemes using thyristor controlled series capacitors [3]. However, few, if any, detailed investigations have been undertaken into the practical suitability of the inverter-based series compensation concept proposed by Gyugyi [4] for the particular purpose of power oscillation damping.